Energy storage and transfer power processor with self-contained parametric regulating loop

ABSTRACT

An energy storage and transfer power processor having an inductive or inertial energy transformer for transferring energy from a power source to a load in repetitive energy transfer cycles each having an energy storage phase during which the transformer stores energy from the power source and an energy delivery phase during which the transformer delivers stored energy to the load. The power processor has its own parametric regulating loop for sensing a control parameter which deviates from a steady state value concurrently with deviation of the processor from an equilibrium condition wherein the energy stored in and the energy delivered by the energy transformer during successive transfer cycles remain equal and constant, such that average stored energy level in the storage means remains constant at a steady state level. The regulating loop regulates the transformer duty cycle in response to departure of the control parameter from its steady state value as a result of changes in the processor input and/or output conditions to instantaneously restore the processor to equilibrium. The invention may be utilized in both electrical and mechanical energy transfer systems to maintain a selected system output quantity at a steady state value which may be fixed or varied by command.

United States Patent [191 Ber-man i111 3,790,816 Feb.5,1974

[. ENERGY STORAGE AND TRANSFER POWER PROCESSOR WITH SELF -CONTAINEDPARAMETRIC REGULATING LOOP Inventor: Baruch Bel-man, Palos VerdesPeninsula, Calif.

Assignee: TRW Inc., Redondo Beach, Calif.

' Filed: Mar. 30, 1972 Appl. No.: 239,568

US. Cl. 307/149, 180/65 R Int. Cl. H02j 7/00 Field of Search 307/149;74/859 References Cited UNITED STATES PATENTS 3/1971 Berman et al.74/859 Primary Examiner-J. R. Scott Assistant Examiner-M. Ginsburg.

Attorney, Agent, or F irm-Daniel J. Anderson; Donald R. Nyhagen; JerryA. Dinardo ABSTRACT An energy storage and transfer power processorhaving an inductive or inertial energy transformer for transferringenergy from a power source to a load in repetitive energy transfercycles each having an energy storage phase during which the transformer.stores energy from the power source and an energy delivery phase duringwhich the transformer delivers stored energy to the load. The powerprocessor has its own parametric regulating loop for sensing a controlparameter which deviates from a steady state value concurrently withdeviation of the processor from an equilibrium-condition wherein theenergy stored in and the energy delivered by the energy transformerduring successive transfer cycles remain equal and constant, such thataverage stored energy level in the 7 Claims, 7 Drawing Figures ENERGYPROCESSOR"? i v I [4 E ENERGY TRANSFORMER i l2 l8 l3 2 i Storage E PowerM ec| ns Source Sensor s tching E Load Means 20 OMMAND i w Duty y le v iv 7/ Controller 9 PAIENTEU 5 SHEEI 2 0? 3 7O 2 72 r 37 Error Command 1Controller Detector Source 38 64 es Power I Pym fl Q Sensor ICommutoring J 22 Circuit Fleld 56 (Energy Battery 5 ruge) Free 42Wheeling Diode 6O -Armoture Command Signal Source Error DetectorController PATENTEBFEB m I 3.790.816

saw a or a 72 70) (62 4 Error Command Detector Source Blocking 64 66Sensor 56 Rectifier 22 g Field (Energy Botteil Power storage)Commu'rcnting Switch IYCUI l 1 so 40 ,7 s 7 MW, M; 38

58 Total Circuit Resistance 24 Free 5 Series Wheeling Fie|d Diode 42Armoture Lood 60f Q 1 ENERGY STORAGE AND TRANSF ER POWER PROCESSOR WITHSELF -CONTAINED PARAMETRIC REGULATING LOOP BACKGROUND OF THEINVENTION 1. Field of the Invention I This invention relates generallyto inductive and inertial energy storage and transfer power processorsof the kind which alternately store energy from a power the load. Suchan energy processor has an inductive or inertial energy transformer,hereafter referred to generically as a kinetic energy transformer orsimply an energy transformer, including an energy storage means andswitching means for effecting energy transfer to the load in repetitiveenergy transfer cycles each having an energy storage phase and an energydelivery phase. During the storage phase of each energy transfer cycle,the storage means stores energy from the power source. During thedelivery phase of each cycle, stored energy from the storage means isdelivered to the load.

The energy storage and transfer power processor has a duty cycle whichisdefined as the ratio of the transfer cycle storage or delivery phaseperiod to the total transfer cycle period. Regulation of this duty cycleregulates the rate of energy transfer and hence the power delivered tothe load during each cycle.

An energy storage and transfer power processor may be utilized in bothelectrical and mechanical energy transfer systems. One example of anelectrical energy transfer system having such a processor is describedin a. paper entitled Battery Powered Regenerative SCR Drive, publishedin the 19-70 edition of the IEEE IGA Conference Record. This drive andother related drives are also discussed in a paper entitled Electric CarDrives Design Considerations," presented to the Society of AutomotiveEngineers, Automotive Engineering Congress, Detroit, Michigan, Jan. -14,1972, and in the references cited in the latter paper. An example of amechanical energy transfer system embodying an energy storage andtransfer processor is an inertial press. Other examples of energytransfer systems are found in the following patents:

The above referenced battery powered drive is a time ratio controlledregenerative battery powered vehicle drive system which may be describedin general terms as having a motor-generator (torquer) connected acrossa storage battery, an inductive energy storage means which may be thefield winding of the torquer, and a power switch for controlling currentflow through the system. The drive system is operable in a regenerativemode and a drive mode. In the regenerative mode, the torquer operates asa generator driven from the output shaft, and the power switch isoperated between alternate off and on states to effect alternate storageof electrical energy from the torquer in theenergy storage means anddelivery of the stored energy plus the output of the torquer to thebattery to charge the battery. In the drive mode, the power switch isagain operated betweenits off and on states to effect alternate storageof electrical energy from the battery in the storage means and deliveryof the stored energy to the torquer which then operates as a motor todrive the output shaft. In drive mode, electrical energy is delivered tothe load (i.e. torquer) to drive the output shaft in the on state of theswitch. In the regenerative mode, energy is delivered to the load (i.e.battery) in the off state of the power switch to charge the battery andproduce braking torque. The ratio of the on time of the switch to thetotal time or period of each off-on cycle of the switch (i.e. off" timeplus on time) is referred to as the duty cycle of the switch. This dutycycle is regulated, to regulate the power delivered to the load, inresponse to actuation of a control, such as a throttle pedal, which isadjustable to command a range of driving torques in the drive mode and arange of braking torques in the regenerative mode.

The inertial press referred to earlier has a motor driven flywheel whichoperates a reciprocating ram through a clutch mechanism. During pressoperation, work material is fed past the ram, and the clutch mechanismis actuated periodically to effect driving of the ram through a workingstroke by the kinetic energy of the rotating flywheel. In this type ofmachine, the flywheel provides an inertial energy storage means in whichenergy is stored by the wheel drive motor and from which energy isperiodically extracted during the working strokes on the ram.

It is apparent from the above discussion that the described systems areenergy transfer systems having a power source, a load, and an energystorage and transfer power processor for transferring energy from thepower source to the load in repetitive energy transfer cycles eachhaving an energy storage phase and an energy delivery phase. During eachstorage phase, energy from the power source is stored in the energystorage means of the processor. During each energy delivery phase,stored energy is transferred from the storage means to the load.

Energy transfer systems of this kind are characterized by a commonproblem with which the present invention is concerned. The problemreferred to involves maintaining the transfer systems in equilibriumduring commanded steady state operation so as to maintain a controlledoutput quantity of the systems at a steady state value. If suchequilibrium is not maintained, the energy transfer process will convergetoward zero output or toward infinite output, limited only by thephysical constrictions of the power source and load, with a resultantwide excursion of the controlled quantity from its steady state value.In this regard, consider the simple example of an inertial punch presspowered by an unregulated drive motor. If parts are stamped at too slowa rate, the flywheel speed will increase to a value limited only by thehorsepower of the driving motor and the energy losses. If parts arestamped at an excessive rate, the flywheel speed will decrease to zero.Accordingly, sustained operation of such a pressin equilibrium speedrequires stamping of parts at a rate which maintains an approximatelyconstant average flywheel speed. 7

Various methods have been devised for maintaining in equilibrium energytransfer systems of the character described. One method, for example,utilizes servo means for regulating the duty cycle of the energy storageand transfer processor in response to changes in the controlledquantity. This control method is not satisfactory, however, because of.the large size of the energy storage means required and the remotelocation, relative to the processor, at which system changes are sensed.This remoteness creates time lags which permit substantial excursions ofthe controlled quantity before corrective action occurs. Another methodof maintaining equilibrium involves the use of a regulated power source.This latter method of control is also unsatisfactory for manyapplications, however, because of the inability or difficulty ofregulating the rate of energy transfer.

SUMMARY OF THE INVENTION The present invention provides an improvedmethod of and means for maintaining in equilibrium energy transfersystems of the class described, that is energy transfer systems whichutilize an inductive or inertial energy storage and transfer powerprocessor including a kinetic energy transformer for transferring energyfrom a power source to a load. More specifically, the invention providesa novel energy storage and transfer power processor, hereafter referredto in places as a power processor or simply a processor, which maintainsitself, and thereby also the energy transfer system embodying theprocessor, in an equilibrium condition. As noted earlier, thisequilibrium condition is one wherein the energy stored in the. energytransformer and the stored energy delivered from the transformer duringsuccessive energy transfer cycles remain equal and constant, such thatthe average stored energy level in the transformer remains at a steadystate level.

To this end, the power processor is provided with its own parametricregulating loop for maintaining equilibrium. This regulating loopincludes means for sensing a control parameter which deviates from asteady state value concurrently with deviation of the processor fromequilibrium and means for regulating the processor duty cycle inresponse to departure of the control parameter from its steady statevalue as a result of changes in the processor input and/or outputconditions and in such a way as to instantaneously restore the processorto equilibrium. The response time of the regulating loop is on the orderof the period of the energy transfer cycles so that restoration of theprocessor to equilibrium occurs without any significant excursions ofthe controlled quantity of the energy transfer system in which theprocessor is used.

The invention may be utilized in both electrical and mechanical energytransfer systems whose rate of energy transfer is either fixed orregulated by command. Depending upon the type of energy transfer systemin which the processor is used and/or the system output quantity to becontrolled, the duty cycle of the processor may be regulated in responsesolely to the control parameter or in response jointly to the controlparameter, the controlled output quantity of the energy transfer systemand/or an operator command.

The invention is described in connection with the battery poweredregenerative vehicle drive system discussed earlier. In thisapplication, the energy storage and transfer processor transfers energybetween the battery and torquer of the drive system. The torquer fieldis utilized as the energy storage means of the processor. The controlparameter in response to which the duty cycle of the processor isregulated by its parametric regulating loop to maintain equilibrium iscurrent flow through the torquer field. The duty cycle is regulated inresponse to both the control parameter and a throttle pedal command toboth regulate the driving or quantity are different as, for example, avehicle drive I system wherein the controlled quantity is torquer speedrather than torque. In fact, systems where the control parameter andcontrol quantity are different must retain the self-contained parametricregulating loop. The control quantity is than used to command theparametric loop.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of theinvention;

FIG. 2 illustrates an energy transfer system embodying the invention;

FIG. 3 is a circuit diagram of a battery powered regenerative vehicledrive embodying the invention showing the drive in its drive mode;

FIG. 4 is a block diagram of the drive in its drive mode;

FIG. 5 is a circuit diagram of the drive in its regenerative mode;

FIG. 6 is a block diagram of the drive in its regenerative mode; and

FIG. 7 is an equivalent circuit diagram of the motorgenerator embodiedin the drive.

DESCRIPTION OF THE PREFERRED EMBODIMENTS References is made first toFIG. 1 illustrating a block diagram of an energy transfer system 10embodying an energy storage and transfer power processor 11 according tothe invention for transferring energy from a power source 12 to a load13. Processor 11 has a kinetic energy transformer 14 including energystorage means 15 and a time ratio switching means 16 for effectingenergy transfer from the power source to the load in repetitive energytransfer cycles each having an energy storage phase during which thestorage means stores energy from the power source and an energy deliveryphase during which the power source and/or storage means deliver energyto the load.

Sustained steady state operation of the energy transfer system 10 isachieved by maintaining the power processor 11 in a condition ofequilibrium, wherein the energy stored in and the stored energydelivered by the processor during successive energy transfer cyclesremain equal. and constant, such that the average stored energy level inthe processor remains at a steady state value. Unless such equilibriumis maintained, the energy transfer process will converge toward zero ortoward infinite output, limited only by the power source and loadconstrictions.

According to the present invention, sustained equilibrium of theprocessor 11 is accomplished by selecting a control parameter whichinstantaneously reflects a departure of the processor from equilibriumand providing the processor with its own parameteric regulating loop 17for regulating the processor duty cycle in response to the controlparameter to restore equilibrium. The control parameter selected is onewhich has a steady state value when the processor is in equilibrium anddeparts from this value in response to and concurrently with any changein the processor input and/or output conditions. Regulating loop 17includes a sensor 18 for sensing the selected control parameterandcontrol means 19 for regulating the processor duty cycle, i.e. ratioof transfer cycle phase period to total transfer cycle period, inresponse to departure of the control parameter from its steady statevalue. This duty cycle regulation restores the processor to equilibriumand thereby the control parameter to its steady state value. The rate ofenergy transfer through the power processor 11 may be relativelyconstant or subject to regulation by command. In the latter case, thecontrol parameter output from the sensor 18 and the command are combinedin an error detector 20 whose output is supplied to the duty cyclecontrol 19. The rate ofenergy transfer, or level of any output quantity,is established by the command, and the regulating loop maintains theprocessor in equilibrium at the energy transfer rate or level of outputquantity established by any given fixed command.

FIG. 2 illustrates an electrical energy transfer system 100 embodying aninductive energy storage and trans fer power processor 110 according tothe invention for transferring electrical energy from a variable lowvoltage d.c. generator (power source) 12a to a higher quasi fixedvoltage battery (load) 13a. The kinetic energy transformer 14a of theprocessor 11a comprises an inductor (energy storage means) 15a in serieswith the generator and battery and a time ratio power switch (switchingmeans) 16a in parallel with the battery. The parametric reguating loop17a of the processor comprises a current sensor (controlparametersensor) 18a in series between the generator and inductor, an errordetector a, and a switch controller (duty cycle controller) 19a foroperating the power switch ON (closed) and OFF (open) positions.

Controller 19a .operates the power switch 16a between its ON and OFFpositions alternatively in such a way that each ON period of the switchis inversely proportional to the error from the detector 2011. Each timethe switch assumes its ON position, electrical energy from the generator12a is stored in the inductor 15a. Each time the switch assumes its OFFposition, the energy stored in the inductor plus the output of thegenerator are delivered to the battry 13a. Thus, the processor 11atransfers energy from the generator 12a to the battery 13a in repetitiveenergy transfer cycles each having an energy storage phase and an energydelivery phase.

In this energy transfer system, equilibrium obviously depends onequilibrium in the inductor 15a, i.e.

( 8) on) a al an where:

V, generator voltage V battery voltage I generator and inductor currentt time power switch is ON (energy storage phase period) t time powerswitch is .OFF (energy delivery phase period) T= t t (total energytransfer cycle period) a (tON/t) (duty cycle) =(V V,,/V5

voltage or the ratio shown in equation (2) drops below a selected steadystate value, the duty cycle must be decreased by. decreasing t tomaintain equilibrium. Conversely, if the differnce between generator andbattery voltage or the ratio in equation (2) rises above its steadystate value, the duty cycle must be increased by increasing t tomaintain equilibrium.

It is evident that the current flow I through the energy transfer system10a reflects such changes in the generator or battery voltage. That isto say, the currentde' creases at an increasing rate with a decreasingdifference between the battery and generator voltages. The currentincreases at an increasing rate with an increasing difference betweenthe battery and generator voltages. The current has an average steadystate value when the system is operating in equilibrium with thegenerator, battery and other transfer elements operating at theirselected steady state values. The parametric regulating loop 17a of thepower processor 11a utilizes the current flow as a control parameter andregulates the duty cycle of the processor in response to departure ofthis control parameter from its steady state value to maintain theprocess and thereby the energy transfer system in equilibrium. Thus, theswitch controller 190, which may be a pulse width modulator controllinga solid state power switch 16a, operates the switch between its OFF andON states alternately and regulates the duration of the ON periods (I ofthe switch in re sponse tothe current flow I through the sensor 18a tomaintain the current at its steady state level and thereby the energytransfer system 10a in equilibrium.

The battery powered regenerative vehicle drive system 20 illustrated inFIGS. 3 through 7 represents another physical implementation of theenergy transfer system of FIG. 1. Except for its inclusion of thepresent equilibrium detection and control invention, the drive system islike that described in the earlier mentioned IEEE paper. The drive hasan electrical storage battery 22, a motor-generator (torquer) 24, and anenergy storage and transfer power processor 26 connecting the batteryand torquer. The torquer 24 is typically a series type d.c. tractionmotor rated for high speed operation and is coupled to the vehicle driveshaft S.

As will be explained in more detail presently, the drive system 20 isoperable in a drive mode (FIGS. 3, 4) and a regenerative mode (FIGS.5,6). In the drive mode, the torquer 24 operates as a motor, and theprocessor 26 delivers pulses of electrical energy from the battery 22 tothe torquer to drive the vehicle drive shaft S. In the regenerativemode, the torquer operates as a generator which is driven from the driveshaft S, as during down hill coasting of the vehicle, and the processordelivers pulses of electrical energy from the torquer to the battery forchanging the battery and braking the vehicle.

Referring to FIG. 3, the power processor 26 comprises a mode controlrelay 28 having contacts 30, 32, 34, 36 for shifting between the driveand regenerative modes, a power switching circuit 37 including an SCRpower switch 38 and a commutating network 40 for the power switch, afree-wheeling diode 42, and a blocking rectifier 44. The commutatingnetwork 40 is required because SCR 38 is utilized as a power switch andbecause of the d.c. operation of the drive and includes a commutatingSCR switch 46, a commutating capacitor 48, a linear inductor 50 with itsdirectional rectifier 51, a saturating reactor 52, and a prechargecircuit 54. As will appear presently, the power switch 38 andcommutating switch 46 are gated on by application of low power gatingsignals to their gates.

In both the drive and regenerative modes of the drive system, thecapacitor 48 is initially charged through the precharge circuit 54. Whenthe commutating SCR 46 is turned ON by application of a low power signalto its gate, with the power switch 38 in its ON state, capacitor 48discharges through the linear inductor 50 while the saturating reactor52 is blocking and resetting magnetically. The linear inductor 50 andcapacitor 48 form a resonant circuit which oscillates at the resonantfrequency of the circuit. During this oscillation, the power stored incapacitor 48 is transferred to the linear inductor 50 which, in turn,delivers the power to the capacitor in a reverse direction. Thisoscillation establishes the common node of the capacitor 48 and thesaturatin g reactor 52 at a voltage approximately equal and opposite tothe battery voltage. Thus, when the saturating reactor saturates, thepower switch 38 and the commutating switch 46 are subjected to a reversevoltage across their terminals. This reverse voltage causes the switches38 and 46 to turn OFF and stop conducting. Capacitor 48 recharges viathe saturated saturable reactor 52, after which the power switch 38 maybe gated ON by applying a gating signal to its gate and the above cyclerepeated. Thus, the power switch 38 may be gated ON and OFF in alternatesequence by applying gating signals alternately to the gates of switches38,

The regenerative drive 20 is shifted between its drive and regenerationmodes by operation of the mode control relay 28. When in the drive mode,the relay contacts 30., 32, 34, 36 are closed to their positions of FIG.3 and the drive 20 assumes its drive configuration illustrateddiagrammatically in FIG. 4. In this drive configuration, the torquer 24and free-wheeling diode 42 are connected in parallel across the battery22 through the power switch 38. As will .be explained in more detailpresently, during operation of the drive system, in its drive mode, thepower'switch 38 is gated ON, and OFF in repetitive energy transfer cycleof duration T. Each time the-power switch gates ON, the output voltby anequivalent or analog circuit comprising an inductor 56 (series field), aseries resistor 58 (total torquer circuit resistance), a large capacitor60 (torquer armature), and a shunt resistor 61, representing the load,connected across the armature. When the power switch gates ON, batterycurrent flow through and stores energy in the field inductor. If thetorquer inductance is high, the energy stored in the inductor 56 duringeach ON period of the power switch will force current to continuecirculating through the torquer armature and field circuit, returningvia the free-wheeling diode 42, during the OFF period of the switchwithout significant decay. Under these conditions, the torquer currentapproaches a d.c. waveform. On the other hand, if the torquer inductanceis small, its energy storage capacity will be small, and energy storedin the torquer field inductor will dissipate rapidly. The torque currentwill thus be discontinuous. Power switch 38 remains ON for a time (Iduring each energy transfer cycle and OFF for the remainder (t of thecycle (T). The ratio of t to T (t t is the duty cycle.

As will be explained presently, the duty cycle a is regulated to bothmaintain the power processor 26 in equilibrium and regulate theelectrical power to the torquer 24. The electrical power delivered tothe torquer 24 is proportional to orv to a first approximation and maybe expressed as P LV [,V, 3

where:

P is the electrical power to the torquer;

I, is the torquer current;

V is the battery voltage;

V, is the average torquer voltage.

From the equation (3) above, it is evident that the duty cycle may beexpressed as a t/ B) The torquer torque is proportional to the torquer'current, and the torquer speed is proportional to the current and dutycycle.

Reference is now made to FIGS. 5 and 6 illustrating the drive 20 in itsregenerative mode. In this mode, the relay contacts 30, 32, 34, 36 areclosed to their positions of FIG. 5 and the drive assumes itsregenerative configuration illustrated diagrammatically in FIG. 6. Thetorquer 24 is driven as a generator from the vehicle drive shaft S anddelivers electrical charging current to the battery 22. Thus, when thetorquer is driven as a generator, a voltage proportional to drive shaftspeed and torquer field flux is developed across the torquer armature.

While the torquer armature voltage varies with drive shaft speed, thebattery 22 and its load remain at a quasi constant voltage level. As thevehicle decelerates, the drive shaft speed and hence armature voltagedecrease. As a consequence, means are required to effectively ladlecharging current from the low armature voltage torquer to the battery.The illustrated drive 20 in its regenerative mode provides anall-electric pump circuit for electrically pumping current from the lowvoltage torquer to the higher voltage battery. In this regard, it willbe seen in FIG. 6 that in the regenerative mode, the torquer 24 andpower switch 38 are connected in parallel across the battery 22 throughthe blocking rectifier 44. Operation of the power switch between its OFFand ON states effects alternate energy storage in the torquer fieldinductor 56 and energy transfer from the field inductor to the battery22. Thus, when the power switch. 38 is ON, energy from the aramture 24is stored in the field inductor 56. When the power switch is OFF, energyproduced by the torquer as well as energy stored in the field inductoris delivered to the battery. The blocking rectifier 44 prevents thebattery from discharging back to the torquer.

In this regenerative mode, the duty cycle a of the drive 20 is expressedby the equation:

01 (I /T) s z/ya) where:

V is the battery voltage;

V, is the average torquer voltage.

The average current I delivered to the battery is expressed by theequation:

where:

I, is the torquer current (average).

At this point, it is evident that the drive system provides an energytransfer system having a power source, a load, and a power processor 26including energy storage means and switching means for transferringenergy from the power source to the load in repetitive energy tranfercycles of fixed duration each having an energy storage phase and anenergy delivery phase. Thus, in the'drive mode of the dirve system 20,the battery 22 provides the power source, the torquer 24 constitutes theload, and the torquer field inductor 56 is the energy storage means. Inthe energy storage phase of each energy transfer cycle, energy from thebattery is stored in the field inductor and is also delivery to powerthe torquer armature. During the energy delivery phase of each cycle,this stored energy is delivered to the torquer to drive the vehicle. Inthe regenerative mode of the drive system 20, the torquer 24 providesthe power source, the battery 22 the load, and the torquer fieldinductor 56 the energy storage means. During the storage phase of eachenergy transfer cycle, energy from the torquer is stored in its fieldinductor. During the energy delivery phase of each cycle, this storedenergy is delivered to the battery to charge the latter and also producea braking torque on the vehicle.

In each mode, the power deliveredto the load is proportional to the dutycycle a and is regulated by varying the duty cycle. Thus, in the drivemode, regulation of the duty cycle varies the power delivered to thetorquer 24 and hence the torque developed by the torquer and vehiclespeed. In the regenerative mode, regulation of the duty cycle varies thepower delivered by the torquer to the battery to charge the latter andhence the braking torque exerted on the vehicle by the torquer. Itshould be noted here that the energy storage device may be any inductor,not necessarily the torquer field, as shown.

Drive system 20 is equipped with a command signal source 62 which inthis instance is a throttle pedal movable between a fully released orretracted position and a fully depressed or extended position. Forconvenience in the ensuing description, the range of pedal positionsbetween the fully retracted and mode transfer positions is referred toas the braking range. The range of pedal positions between the modetransfer and fully depressed positions is referred to as the drivingrange. Throttle pedal control 62 operates a switch or the like whichactuates the mode control relay 28 to its drive condition when thethrottle pedal is within the driving range and to its regenerationcondition when the pedal is within its braking range.

As will be explained in more detail shortly, the throttle pedal control62 provides a torque command signal related to the throttle pedalposition for controlling the drive system 20. Thus, when the throttlepedal is depressed through its driving range from the mode transferposition to the full depressed or maximum torque position, the throttlepedal control commands increasing driving torque. This increasingdriving torque command effects an increase, at a controlled rate, of thedriving mode duty cycle to increase the driving torque developed by thetorquer 24 until the developed torque equals the commanded torque.Return ,of th throttle pedal to its mode transfer position has theopposite effect of reducing the driving torque. Similarly, when thethrottle pedal is retracted through its braking range from the modetransfer position to its fully retracted or maximum braking position,-the throttle pedal control 62 commands increasing braking torque. Thisincreasing braking torque command effects an increse of the regenerativemode duty cycle to increase the braking torque developed by the torqueruntil the developed braking torque'equals the commanded braking torque.Depression of the throttle pedal from its fully retracted position toits mode transfer position has the opposite effect of reducing thebraking torque.

From the description to this point,-it is evident that in any givenfixed position of the throttle pedal, the drive system 20 should operatein a condition of steady state equilibrium, wherein the driving torqueor braking torque, as the case may be depending upon the operating modeof the drive system, developed by the torquer 24 remains constant at thelevel commanded by the throttle pedal position. This equilibriumcondition is achieved by maintaining the processor 26 in an equilibriumcondition wherein the energy stored and delivered by the processorduring each energy transfer cycle remain equal to one another and at theproper level to establish a developed torque in the torquer armature 24equal to the torque commanded by thethrottle pedal position. Under theseconditions, the average stored energy level in the energy storage meansremains substantially constant- As in the earlier embodiments, powerprocessor 26 has its own parametric regulating loop 64 for maintainingequilibrium by continuously sensing a control parameter which has agiven steady state value when the drive system is in steady equilibrium,and regulating the duty cycle of the system in response to deviation ofthe parameter from its steady state value in such a way as to restorethe system to equilibrium.

'field inductor 56. The duty cycle is regulated in response to deviationof the torquer current from its steady state value in order to maintainthe drive system in equilibrium at any given torque level commanded bythe throttle pedal control 62 by varying the period (I of the energystorage phase of each energy storage cycle. In the drive mode of thedrive system, the duty cycle is thus regulated to satisfy equation (4)supra. In the regeneration modes the duty cycle is regulated to satisfyequation (5).

To the above ends, the regulating loop 64 is equipped with a currentsensor 66 in series with the torquer field inductor 56. Sensor 66produces an output proportional to the current flow through the torquerfield.

The output of sensor 66 is connected to an error detector 70 whichreceives an additional input, hereafter referred to as a torque commandsignal, from the command signal source or throttle pedal control 62.This torque command signal is a signal representing the driving torqueor braking torque, as the case may be, corresponding to the throttlepedal position.

The output of error detector 70 is a signal representing the differencebetween the sensor and torque command signals to'the detector. Thisoutput signal is fed to a power switch controller 72, such as a pulsewidth modulator, having outputs connected to the gates of power switch38 and commutating switch 46. The switch controller feeds to the powerand commutating switches gating signals for gating the switches ON andOFF in such a way as to establish a duty cycle a related to theamplitude of the input signal to the controller. More specifically, thecontroller feeds to the power switch 38 a gating signal having periodicgating pulses which gate the power switch ON for a period I proportionalto the amplitude of the controller input signal. The controller feeds tothe commutating switch 46 a gating signal having periodic gating pulseswhich occur between the gating pulses to the power switch and gate thecommutating switch ON and thereby the power switch OFF for a period suchthat each power switch time ON, t pulse and the following power switchtime OFF, 2 have a total or combined period T.

The operation of the drivesystem will now be described, assuming thethrottle pedal to be initially in its fully released or retractedposition with the vehicle stationary. Under these conditions, the modecontrol relay contacts 30, 32, 34, and 36 occupy their regenerationpositions of FIGS. 5 and 6, the power switch 38 is OFF, the torquer 24is stationary, and no current flow occurs in the drive system.

Assume now that the throttle pedal is depressed through its modetransfer position to a final position in its driving range correspondingto a selected driving torque of the motor 24. As the pedal passesthrough its mode transfer position, the pedal control 62 actuates themode control relay 28 to shift its contacts to their drive positions ofFIGS. 3 and 4 and feeds to the error detector 70 a torque command signalwhich progressively increases to a level representing the motor torquecommanded by the final pedal position. Switch controller 72 thendelivers to the power switch 38 and commutating switch 46 gating signalswhich gate the power switch ON and OFF to deliver energizing current tothe torquer 24 in the earlier described energy transfer cycles andthereby accelerate the vehicle with a driving torque equal to thecommand torque. During cruising with the throttle pedal in afixed driveposition, such that the error detector receives a fixed torque commandsignal, the regulating loop 64 of the power processor 26 operates toregulate the processor duty cycle in response to the control parameter(current flow through the torquer field inductor 56) to maintain theprocessor in an equilibrium condition wherein the energy stored and theenergy delivered to the torquer during successive transfer cycles remainequal and con-.

stant. I

Braking of the vehicle is accomplished by effecting retraction of thethrottle pedal to its braking range to shift the contacts of the modecontrol relay 28 to their regenerative or braking positions of FIGS. 5and 6. The torquer 24 is then driven as a generator from the drive shaftS and delivers charging current through the power processor 26 to thebattery 22 in the earlier described energy transfer cycles. The torquerthereby also produces a braking torque for decelerating the vehicle. Inthis braking mode with the throttle pedal in a fixed braking position,the regulating loop 64 of the power processor 26 operates to regulatethe processor duty cycle in response to the .control parameter (currentflow through the torquer field inductor) to maintain the processor in anequilibrium condition wherein the energy stored and the energy deliveredto the battery during successive energy transfer cycles remain equal andconstant.

The power switch controller 72 may comprise any suitable circuitry fordelivering gating signals to the power and commutating switches 38, 46in the manner explained. By way of example, this controller may comprisea clock pulser and variable time pulser similar to those described inthe earlier mentioned US. Pat. No. 3,566,717.

In the drive system of FIGS. 3 through 7, the control parameter which issensed to maintain the power processor in equilibrium and the outputquantity of the system which is controlled to retain it at a steadystate level by maintaining equilibrium are the same, namely torquercurrent or torque. However, in other applications, the control parameterand controller quantity may be different quantities.

What is claimed as new in support of Letters Patent is:

1. The method of delivering energy from a power source to a load whichcomprises the steps of:

coupling an energy storage means to said source and load alternately toeffect energy transfer from said source to said load in repetitiveenergy transfer cycles each having an energy storage phase during whichsaid storage means receives and stores energy from said source and anenergy delivery phase during which said storage means delivers storedenergy to said load, whereby the energy transfer occurs in periodicfashion with a duty cycle which equals the ratio of one transfer cyclephase period to the total transfer cycle period and which duty cycle maybe regulated to maintain an equilibrium condition wherein the energystored in and the energy delivered by said storage means duringsuccessive energy transfer cycles remain substantially equal andconstant such that the average stored energy level in said storage meansremains substantially constant at a steady state level;

sensing a control parameter which deviates from a steady state value inresponse to and concurrently with deviation of said average storedenergy level from said steady state level; and

regulating said duty cycle in response to said control parameter tomaintain said equilibrium condition.

2. The method of claim 1 wherein:

said energy is electrical energy; and

said control parameter is an electrical quantity related to the storedenergy level in said storage means.

3. The method of claim 2 wherein:

said storage means comprises and electrical inductor;

and

said control parameter is current flow through said inductor.

4. An energy transfer system for transferring energy from a power sourceto a load comprising:

energy transfer means including input means for connection to said powersource, output means for connection to said load, energy storage means,and time ratio means for effecting energy transfer from said input meansto said output means in repetitive energy transfer cycles each havingand energy storage phase during which said storage means receives andstores energy supplied to said input means and an energy delivery phaseduring which said storage means delivers stored'energy to said outputmeans, whereby said transfer means has a duty cycle which equals theratio of one transfer cycle phase period to the total transfer cycleperiod and which duty cycle may be regulated to maintain an equilibriumcondition wherein the energy stored in and the energy delivered by saidstorage means during successive energy transfer cycles remainsubstantially equal and constant such that the average stored energylevel in said storage means remains substantially constant at a steadystate level; means for sening a control parameter which deviates from asteady state value in response to and concurrently with a deviation ofsaid average stored energy level from said steady state level; and

means for regulating said duty cycle in response to said controlparameter to maintain said equilibrium condition.

5. An energy transfer system according to claim 4 wherein:

said power source and load comprise an electrical power source and anelectrical load, respectively; said storage means comprises anelectrical energy storage means;

said time ratio means comprises electrical switching means operablealternately to one state to connect said storage means to said inputmeans and to another state to connect said storage means to said outputmeans;

said control parameter is an electrical quantity related to the storedenergy level in said storage means.

6. An energy transfer system according to claim 5 wherein: said storagemeans comprises an electrical inductor.

7. An energy transfer system according to claim 6 wherein: said controlparameter is current flow through said inductor.

1. The method of delivering energy from a power source to a load whichcomprises the steps of: coupling an energy storage means to said sourceand load alternately to effect energy transfer from said source to saidload in repetitive energy transfer cycles each having an energy storagephase during which said storage means receives and stores energy fromsaid source and an energy delivery phase during which said storage meansdelivers stored energy to said load, whereby the energy transfer occursin periodic fashion with a duty cycle which equals the ratio of onetransfer cycle phase period to the total transfer cycle period and whichduty cycle may be regulated to maintain an equilibrium condition whereinthe energy stored in and the energy delivered by said storage meansduring successive energy transfer cycles remain substantially equal andconstant such that the average stored energy level in said storage meansremains substantially constant at a steady state level; sensing acontrol parameter which deviates from a steady state value in responseto and concurrently with deviation of said average stored energy levelfrom said steady state level; and regulating said duty cycle in responseto said control parameter to maintain said equilibrium condition.
 2. Themethod of claim 1 wherein: said energy is electrical energy; and saidcontrol parameter is an electrical quantity related to the stored energylevel in said storage means.
 3. The method of claim 2 wherein: saidstorage means comprises and electrical inductor; and said controlparameter is current flow through said inductor.
 4. An energy transfersystem for transferring energy from a power source to a load comprising:energy transfer means including input means for connection to said powersource, output means for connection to said load, energy storage means,and time ratio means for effecting energy transfer from said input meansto said output means in repetitive energy transfer cycles each havingand Energy storage phase during which said storage means receives andstores energy supplied to said input means and an energy delivery phaseduring which said storage means delivers stored energy to said outputmeans, whereby said transfer means has a duty cycle which equals theratio of one transfer cycle phase period to the total transfer cycleperiod and which duty cycle may be regulated to maintain an equilibriumcondition wherein the energy stored in and the energy delivered by saidstorage means during successive energy transfer cycles remainsubstantially equal and constant such that the average stored energylevel in said storage means remains substantially constant at a steadystate level; means for sening a control parameter which deviates from asteady state value in response to and concurrently with a deviation ofsaid average stored energy level from said steady state level; and meansfor regulating said duty cycle in response to said control parameter tomaintain said equilibrium condition.
 5. An energy transfer systemaccording to claim 4 wherein: said power source and load comprise anelectrical power source and an electrical load, respectively; saidstorage means comprises an electrical energy storage means; said timeratio means comprises electrical switching means operable alternately toone state to connect said storage means to said input means and toanother state to connect said storage means to said output means; saidcontrol parameter is an electrical quantity related to the stored energylevel in said storage means.
 6. An energy transfer system according toclaim 5 wherein: said storage means comprises an electrical inductor. 7.An energy transfer system according to claim 6 wherein: said controlparameter is current flow through said inductor.